Fate of neonicotinoids in the environment : why bees are threatened

Aseperi, Adeniyi K., Busquets, Rosa, Cheung, Philip C. W., Hooda, Peter S. and Barker, James (2022) Fate of neonicotinoids in the environment : why bees are threatened. In: Núñez-Delgado, Avelino and Arias-Estévez, Manuel, (eds.) Emerging pollutants in sewage sludge and soils. Cham, Switzerland : Springer. (The handbook of environmental chemistry, (114)) ISSN (print) 1867-979X ISBN 9783031076084 (In Press)

Abstract

Pollinators are vital for ecosystems, agriculture and the economy. Their population has been declining over several decades and the current situation is serious and of great concern. Multiple stressors are likely to have contributed to this, and exposure to neonicotinoid pesticides is one possible causative factor. Pollinators, including bees, can encounter neonicotinoids when foraging contaminated flowers, and although they were not the target organism for such pesticides, neonicotinoids can be fatal for them (lethal dose that will reduce the insect population by 50% is ~2 mg/kg). The specific application of these pesticides plays an important role in their dispersion into the environment and application to the seed coating itself provides a more targeted way to release the pesticide with a reduced risk. Neonicotinoids can disperse via aerosols (when sprayed), bound to soil dust and dust abrasion from the seed coating, via the degradation of contaminated plants or run-off from crops treated with the pesticide. They have high solubility in water (e.g. 39.8 g dinotefuran/L, 4.1 g thiamethoxam/L) and this favours their spread, however natural factors such as sunlight, warm weather and microorganisms can degrade them and reduce their persistence. The time required for the concentration of neonicotinoids in soil to reach half of their initial concentration is varied (e.g. 3.4–7,000 days). Soils that are poor in organic matter will poorly retain neonicotinoids and as a result they will be very mobile in them and potentially pollute water systems. In contrast, soils rich in organic matter will have greater retention of neonicotinoids and once saturated, neonicotinoids will leach in a sustained manner. The benefits given by neonicotinoids explain why they are widely used across the globe. Their potential impact in the fields on bees and pollinators in general thus calls for a globally responsible and restricted use of neonicotinoids as well as innovation to reduce their ecotoxicity.

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